The present invention relates to an apparatus and a method for refurbishing abrasive polishing pads used in chemical-mechanical planarization of semiconductor wafers.
Chemical-mechanical planarization (xe2x80x9cCMPxe2x80x9d) processes remove material from the surface of a semiconductor wafer in the production of integrated circuits. FIG. 1 schematically illustrates a CMP machine 10 with a platen 20, a wafer carrier 30, a polishing pad 40, and a planarizing liquid 44 on the polishing pad 40. The polishing pad 40 may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a new generation fixed-abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid 44 may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the wafer, or the planarizing liquid 44 may be a planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed-abrasive polishing pads.
The CMP machine 10 also has an under-pad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the polishing pad 40. A drive assembly 26 rotates the platen 20 (as indicated by arrow A), or it reciprocates the platen back and forth (as indicated by arrow B). Since the polishing pad 40 is attached to the under-pad 25, the polishing pad 40 moves with the platen 20.
The wafer carrier 30 has a lower surface 32 to which a wafer 12 may be attached, or the wafer 12 may be attached to a resilient pad 34 positioned between the wafer 12 and the lower surface 32. The wafer carrier 30 may be a weighted, free-floating wafer carrier; or an actuator assembly 36 may be attached to the wafer carrier to impart axial and/or rotational motion (as indicated by arrows C and D, respectively).
To planarize the wafer 12 with the CMP machine 10, the wafer carrier 30 presses the wafer 12 face-downward against the polishing pad 40. While the face of the wafer 12 presses against the polishing pad 40, at least one of the platen 20 or the wafer carrier 30 moves relative to the other to move the wafer 12 across the planarizing surface 42. As the face of the wafer 12 moves across the planarizing surface 42, material is continuously removed from the face of the wafer 12.
One problem with CMP processing is that the throughput may drop, and the uniformity of the polished surface on the wafer may be inadequate, because waste particles from the wafer accumulate on the planarizing surface 42 of the polishing pad 40. The problem is particularly acute when planarizing doped silicon oxide layers because doping softens silicon oxide and makes it slightly viscous as it is planarized. As a result, accumulations of doped silicon oxide glaze the planarizing surface of the polishing pad with a coating that substantially reduces the polishing rate over the glazed regions.
To return the polishing pads to an adequate state for planarizing additional wafers, the polishing pads are typically conditioned by removing the accumulations of waste matter with an abrasive disk. Conventional abrasive conditioning disks are generally embedded with diamond particles, and they are mounted to a separate actuator on a CMP machine that sweeps them across the polishing pad. Typical abrasive disk pad conditioners remove a thin layer of the pad material itself in addition to the waste matter to form a new, clean planarizing surface on the polishing pad. Some abrasive disk pad conditioners also use a liquid solution that dissolves some of the waste matter as the abrasive disks abrade the polishing surface.
Although conventional diamond-embedded abrasive disks are well suited to condition conventional polishing pads, they may not be well suited to condition the new generation of fixed-abrasive polishing pads. Fixed-abrasive polishing pads generally have exposed abrasive particles across their planarizing surfaces. Additionally, fixed-abrasive pads may have topographical features across their planarizing surface. When a fixed-abrasive polishing pad is conditioned with a diamond-embedded abrasive disk, the diamonds not only remove waste matter material, but they also remove abrasive particles and may damage other features on the planarizing surface of the polishing pad. Conditioning a fixed-abrasive polishing pad with a diamond-embedded disk will likely alter the planarizing surface, and thus the planarizing properties, of the polishing pad. Therefore, conventional pad conditioning processes do not work with the new generation of fixed-abrasive polishing pads.
The present invention is an apparatus and method for refurbishing abrasive polishing pads. In one embodiment, the refurbishing device has an arm positionable over the planarizing surface of the polishing pad, a refurbishing element attached to one end of the arm, and an actuator connected to the other end of the arm. The refurbishing element has a non-abrasive contact medium engageable with the planarizing surface of the polishing pad that does not abrade or otherwise damage raised features on the fixed-abrasive pad under desired conditioning down forces. The actuator moves the arm downwardly and upwardly with respect to the planarizing surface to engage and disengage the non-abrasive contact medium with the planarizing surface of the polishing pad. In a preferred embodiment, the refurbishing device also has a conditioning solution dispenser positionable proximate to the planarizing surface of the polishing pad to dispense a liquid conditioning solution onto the planarizing surface. The conditioning solution is selected from a liquid that reacts with the particular waste matter material to allow the non-abrasive contact medium to remove waste matter material from the polishing pad. As the refurbishing element engages the planarizing surface in the presence of the conditioning solution, at least one of the refurbishing element or the polishing pad moves with respect to the other. In operation, the conditioning solution and the refurbishing element remove waste matter from the pad without abrading or otherwise damaging the planarizing surface of the polishing pad.
In a preferred embodiment, a planarizing machine for chemical-mechanical planarization of a semiconductor wafer has a platen mounted to a support structure and a fixed-abrasive polishing pad positioned on the platen. The fixed-abrasive polishing pad has a suspension medium, a plurality of abrasive particles fixedly dispersed in the suspension medium, and a planarizing surface with exposed abrasive particles. The planarizing machine also has a movable wafer carrier adapted to hold the wafer and engage the wafer with the planarizing surface of the polishing pad. At least one of the platen or the wafer carrier moves with respect to the other to impart relative motion between the wafer and the planarizing surface of the polishing pad. In one embodiment, the planarizing machine has a refurbishing element carriage positioned proximate to the polishing pad, a non-abrasive refurbishing element attached to the carriage, and a solution dispenser positioned proximate to the pad. The refurbishing element carriage has an arm positionable over the planarizing surface and an actuator for moving the arm towards or away from the planarizing surface. The non-abrasive refurbishing element is preferably attached to the arm of the carriage.
In operation, the carriage moves the non-abrasive refurbishing element into engagement with the planarizing surface of the polishing pad as at least one of the carriage and the polishing pad moves with respect to the other to impart relative motion therebetween. A conditioning solution selected to dissolve or oxidize the waste matter material is simultaneously deposited onto the polishing pad. The conditioning solution breaks down the waste matter so that the non-abrasive refurbishing element can remove the waste matter material from the polishing pad without damaging the planarizing surface.
In a method of conditioning a fixed-abrasive polishing pad in accordance with the invention, a conditioning solution that dissolves, oxidizes, or otherwise breaks down the waste matter material is deposited onto at least a portion of the planarizing surface of the fixed-abrasive polishing pad. A non-abrasive refurbishing element is pressed against the planarizing surface in the presence of the conditioning solution, and at least one of the fixed-abrasive polishing pad or the non-abrasive refurbishing element is moved with respect to the other to impart relative motion therebetween. As the refurbishing element moves against the planarizing surface, the conditioning solution and the non-abrasive refurbishing element remove the waste matter material from the planarizing surface without eroding the topography of the planarizing surface.